This invention relates to a power transmission belt in which a canvas is provided on the back of an endless belt base.
Recently, accompanied by requirement for a compact engine, layout of belt is restricted. Especially, in a V-ribbed belt, a layout in such a faction the back of the belt is used as a friction face to friction-contact to a pulley is mostly employed.
In such a V-ribbed belt, a back canvas is usually provided on the back of the belt for reinforcement. It is well known, as disclosed in Laid Open unexamined Japanese Patent Application No. 4-151048, that such a back canvas is abutted and seamed at a joint part thereof by a sewing machine. The machine sewing thread used for the V-ribbed belt is made of cotton fiber, nylon fiber, aramid fiber and the like.
In the case where the joint part of the back canvas is abutted and seamed by a sewing machine, an abutting joint part c is formed by a sewing machine at formation of the canvas, as shown in FIG. 5. When the abutting Joint part is formed, the machine sewing thread already separates (floats) from the surface of the canvas b because of the rigidity thereof to be arched. Therefore, when a belt a (e.g., V-ribbed belt) with the canvas b is molded and vulcanized, the machine sewing thread d has an irregular seam pattern, as shown in FIG. 6, because of the floating. The floating machine sewing thread d is compressed to thus be fallen and warped, then is vulcanized with this state. When the vulcanized belt d is taken out from dies, the machine sewing thread d floats again from the surface, as well as the initial stage, because of the rigidity thereof.
In a case where the belt is arranged in such a fashion that the back of the belt faces inward, the machine sewing thread d deviates from the back canvas b to displace upward at the abutting joint part c of the back canvas b of the belt a, as shown in FIG. 8, which is generally called "floating". The floating machine sewing thread d interferes with a pulley at meshing to cause friction noise and vibration.